I created a 3D Box (rectangle with thickness) to see if this and the 3D polygon object (created previously) could be added together, only to discover there aren't any 3D Modify tools, so I tried the 2D Add. The program locked up, or so I thought. A warning dialog had popped under the program (Select an object for Boolean operation). I suspect a real user would be shutting down the program via Task Manager, losing their work and never notice the warning (if many programs are running). Once the objects were reset to "0" Thickness, 2D Add worked. It seems kind of limiting to not have 3D Boolean tools in the Pro edition.
V18.104.22.168 64-bit RedSDK